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Old 2nd January 2002, 05:59 AM   #1
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Default Subwoofer variable phase control

I am looking for a schematic for a variable phase control as found on commercial subwoofer amps ...

Most diyer's seem to just use a 0/180 degree control but i would like a little more control than that say 15degree intervals or so...

Whats involved?
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Old 3rd January 2002, 12:20 PM   #2
ergo is offline ergo  Estonia
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I think it is something like this that is used (found it from the net somewhere)

***********

Phase shifter circuit
(From Richard Karlquist)
Here is a well known op-amp phase shifter. I am surprised no one has posted it yet, so I guess I will have to. The circuit will have 90 degrees phase shift at:
FREQ = 1/(2*PI*R3*C)

At low frequencies it has 0 degrees of phase shift and at high frequencies it has 180 degrees of phase shift. By making R3 a pot, you can vary the phase at a given frequency from nearly 0 to nearly 180 degrees. Since you want to work at 1 MHz., you will need to use a high frequency op amp, like the Burr-Brown OPA620.

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Old 3rd January 2002, 12:24 PM   #3
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thanks ergo,

I am familiar with such circuits but am unwilling to use them because as stated in your post the phase changes with frequency... i want something that is independant of frequency and can go from 0degrees to 180degrees in 15degree increments.
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Old 3rd January 2002, 08:21 PM   #4
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Maybe you would like to try a circuit that looks
like this:
Attached Images
File Type: png phase.png (1.7 KB, 622 views)
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Old 4th January 2002, 02:19 AM   #5
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Anyone know what values i should use in the schematic mr pass has contributed ... i am currently lacking decent spice software will this circuit provide constant phase adjustment independant of frequency (@ least between 10Hz and 200Hz)?
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Old 4th January 2002, 07:12 PM   #6
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No, the phase is frequency dependent.

What makes you want constant phase vs frequency?
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Old 4th January 2002, 11:59 PM   #7
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i'll just do it in DSP .... i feel that this will cause me less pain.

I want constant phase vs frequency cause i'd like the effect to be the same across the whole bandpass region

I know its really only the phase @ the crossover region that matters in this case but why not go all out.
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Old 7th January 2002, 08:39 PM   #8
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More often people want a constant delay, which
is not the same thing.
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Old 7th January 2002, 11:05 PM   #9
Won is offline Won
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In fact, what AF describes is linear phase.
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Old 8th January 2002, 10:24 AM   #10
Geoff is offline Geoff  United Kingdom
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If it's delay you're after, download the article sb80-3wy.zip at:

http://www.linkwitzlab.com/publications.htm

Geoff
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